Backlight for liquid crystal display and lighting control method therefor

Abstract

A backlight used for a liquid crystal display including a plurality of liquid crystal display elements arranged in a matrix of n rows and m columns, in which constant-time row scanning is performed in row order to change the optical transmittance of the liquid crystal display elements includes a plurality of electron-emitting elements and a phosphor. Each of the electron-emitting elements is disposed so as to face a liquid crystal display element group including a plurality of adjacent liquid crystal display elements with the phosphor therebetween. An electron emission voltage is applied to electron-emitting elements facing liquid crystal display elements for which the row scanning is completed and whose optical transmittance becomes constant. The electron-emitting elements apply electrons to the phosphor. The phosphor is irradiated with electrons, and emits light to the liquid crystal display elements whose optical transmittance becomes constant.

1 . A backlight used for a liquid crystal display including a plurality of liquid crystal display elements arranged in a matrix of n rows and m columns, in which constant-time row scanning is performed for all rows in row order in a frame period to change the optical transmittance of the plurality of liquid crystal display elements, thereby switching an image to be displayed by the plurality of liquid crystal display elements, the backlight comprising: 
 an electron-emitting device comprising a plurality of electron-emitting elements including: 
 an emitter section formed of a dielectric material;  
 a lower electrode disposed below the emitter section; and  
 an upper electrode disposed above the emitter section so as to face the lower electrode with the emitter section therebetween, the upper electrode having a plurality of fine through-holes,  
 wherein the electron-emitting elements accumulate a large number of electrons in the emitter section when a predetermined write voltage is applied between the upper electrode and the lower electrode, and emit the electrons accumulated in the emitter section through the fine through-holes from the emitter section when a predetermined electron emission voltage is applied between the upper electrode and the lower electrode, and  
 the electron-emitting elements are arranged in a matrix so that each of the electron-emitting elements faces each of liquid crystal display element groups including a plurality of the liquid crystal display elements of the liquid crystal display that are adjacent to each other;  
 a phosphor disposed between the upper electrode of the electron-emitting elements and the liquid crystal display so as to face the upper electrode, the phosphor emitting light toward the liquid crystal display by collisions with electrons; and  
 a drive voltage applying circuit for, in a period from the time when the row scanning for one of the liquid crystal display element groups is finished after which the optical transmittance of liquid crystal display elements belonging to the one liquid crystal display element group becomes constant to the time when the row scanning for the one liquid crystal display element group is started next time, applying the electron emission voltage to an electron-emitting element in the plurality of electron-emitting elements for a predetermined time, the electron-emitting element facing the one liquid crystal display element group, and applying the write voltage in a period until the next time when the electron emission voltage is applied again to the electron-emitting element to which the electron emission voltage is applied.  
   
   
   
       2 . The backlight according to  claim 1 , wherein the value n is a multiple of an integer N of 2 or more, 
 the value m is a multiple of an integer M of 2 or more,    the liquid crystal display element groups are arranged in a matrix of n/N rows and m/M columns, n/N being given by dividing n by N, m/M being given by dividing m by M, and    the drive voltage applying circuit is configured to, in a sub-frame period starting at the time when the row scanning for all of the liquid crystal display elements forming one of the liquid crystal display element groups is completed and ending at the time when a time needed for the row scanning for the n/N rows has elapsed since the starting time, apply the write voltage and the electron emission voltage to the electron-emitting element facing the liquid crystal display element group including the liquid crystal display elements for which the row scanning is to be started at the end of the sub-frame period.    
   
   
       3 . The backlight according to  claim 1 , wherein the drive voltage applying circuit is configured to set the write voltage to a voltage according to the optical transmittance of the plurality of liquid crystal display elements belonging to the liquid crystal display element group facing the electron-emitting element to which the write voltage is applied.  
   
   
       4 . A lighting control method for a backlight used for a liquid crystal display including a plurality of liquid crystal display elements arranged in a matrix of n rows and m columns, in which constant-time row scanning is performed for all rows in row order in a frame period to change the optical transmittance of the plurality of liquid crystal display elements, thereby switching an image to be displayed by the plurality of liquid crystal display elements, the backlight comprising an electron-emitting device comprising a plurality of electron-emitting elements including an emitter section formed of a dielectric material, a lower electrode disposed below the emitter section, and an upper electrode disposed above the emitter section so as to face the lower electrode with the emitter section therebetween, the upper electrode having a plurality of fine through-holes, wherein the electron-emitting elements accumulate a large number of electrons in the emitter section when a predetermined write voltage is applied between the upper electrode and the lower electrode, and emit the electrons accumulated in the emitter section through the fine through-holes from the emitter section when a predetermined electron emission voltage is applied between the upper electrode and the lower electrode, and the electron-emitting elements are arranged in a matrix so that each of the electron-emitting elements faces each of liquid crystal display element groups including a plurality of the liquid crystal display elements of the liquid crystal display that are adjacent to each other; and a phosphor disposed between the upper electrode of the electron-emitting elements and the liquid crystal display so as to face the upper electrode, the phosphor emitting light toward the liquid crystal display by collisions with electrons, 
 the lighting control method comprising, in a period from the time when the row scanning for one of the liquid crystal display element groups is finished after which the optical transmittance of liquid crystal display elements belonging to the one liquid crystal display element group becomes constant to the time when the row scanning for the one liquid crystal display element group is started next time, applying the electron emission voltage to an electron-emitting element in the plurality of electron-emitting elements for a predetermined time, the electron-emitting element facing the one liquid crystal display element group, and applying the write voltage in a period until the next time when the electron emission voltage is applied again to the electron-emitting element to which the electron emission voltage is applied.    
   
   
       5 . The lighting control method for the backlight according to  claim 4 , wherein the value n is a multiple of an integer N of 2 or more, the value m is a multiple of an integer M of 2 or more, the liquid crystal display element groups are arranged in a matrix of n/N rows and m/M columns, n/N being given by dividing n by N, m/M being given by dividing m by M, and 
 in a sub-frame period starting at the time when the row scanning for all of the liquid crystal display elements forming one of the liquid crystal display element groups is completed and ending at the time when a time needed for the row scanning for the n/N rows has elapsed since the starting time, the write voltage and the electron emission voltage are applied to the electron-emitting element facing the liquid crystal display element group including the liquid crystal display element for which the row scanning is to be started at the end of the sub-frame period.    
   
   
       6 . The lighting control method for the backlight according to  claim 4 , wherein the write voltage is set to a voltage according to the optical transmittance of the plurality of liquid crystal display elements belonging to the liquid crystal display element group facing the electron-emitting element to which the write voltage is applied.